Question for NASA Tom, or anyone who knows FOR SURE (Minelab sensitivity function)

NASA Tom --

You told me before that on an F70, when you vary sensitivity, you are only altering the RECEIVED signal, NOT the transmit power of the machine.

Is it the same on the Minelab Explorer series? I read in Andy Sabisch's book something that I interpreted to say that sensitivity adjustment does alter the transmit signal, but others have said otherwise. Can you (or anyone) clear this up definitively for me?

Thanks,

Steve

I can (almost) positively say that ..... the 'Sensitivity' function of the Explorer/E-Trac still.......only adjusts the "Receive" sensitivity. I do not believe it alters (increases) 'transmit' power. This would be a 'more parts' and 'more expensive' function. I don't have blueprints of the Minelab(s)....... but can't imagine Transmit power being changed ... with the Sensitivity function.

Thank you, sir. Answers my question!

Steve

I forgot to mention, but the reason I asked is there was some discussion about this on another one of the forums. I do know that when I adjust from semi-auto to manual sensitivity, or likewise adjust upward the level of sensitivity when running manual, I can ABSOLUTELY notice a substantial increase in "iron falsing." I was running in semi-auto 26 just today, for instance (lots of iron and hard to keep a stable threshold). I hit an iffy signal that I thought could be a deep coin -- so I switched to manual sensitivity to see if I could "see" the target better. IMMEDIATELY, the conductive and ferrous numbers changed on the machine -- with an abundance of "31 conductivity" numbers now showing up -- which almost always is iron falsing (31 is the highest conductivity number on an Explorer). These 31s were abundant, but were NON-EXISTENT in semi-auto. I don't know if other things are going on when running semi-auto, but I certainly got different numbers with the higher, manual sensitivity. Given things like this (changing VDI numbers), and the what seems to be a noticeable increase in depth you get with these machines by running sensitivity higher, I wondered...

Steve

The Etrac depth performance is significantly increased with increasing sensitivities. In addition, VID significantly improves and iron falsing significantly decreases with decreasing sensitivities. The Etrac is a perfectly stable, highly accurate (albeit not-too-deep) unit running in full auto mode.

The F75 LTD depth performance is marginally increased with increasing sensitivities. In addition, in my Southern red clay, VID and iron falsing are unchanged with varying sensitivities. I like that characteristic.

Primarily due to F75 being a single-freq unit. Inherent characterisitc is that single-freq units (in general) handle iron much better.

Don't have any technical knowledge but from field experience and reading the Explorer forums you can get arguments either way rel the Explorer as to what works for better depth. I do know it depends on the expertise of the operator and his other facet settings along with the ground (mineralization) which has to be dealth in the equasion.
Speaking for the Explorer only as F series is not my cup of tea even though I have used them.

go-rebels --

Your statements reflect my experiences exactly -- which is why I wondered about the "transmit power" issue. Varying sensitivity on my F-70 seemed not to have that much effect on "depth." Meanwhile, there is much more apparent effect on depth by increasing sensitivity with the FBS machines -- but also more falsing and worse ID. Those noticeable changes are why I sensed that "something different" occurs when adjusting sensitivity upward on an FBS machine, versus an F-series machine.

NASA-Tom -- you are saying that this is primarily due to the multiple frequencies in the FBS plaform versus the single frequency F- machines? Interesting, though I don't understand...it sure seems like SOMETHING happens when you increase sensitivity, which affects depth, ID, falsing, etc. It sure SEEMS like you are increasing the "output power." Is it easy to explain in layman's terms how it's a "multi-frequency" thing, that causes these changes in performance when raising sens. (as opposed to an increase in "transmit power" that I thought might have been happening?)

Also interesting, is that after using both, I will say that I have NOT, for whatever reason, gotten the feeling that the Explorer "handles" iron "worse" than my F-70, at least with respect to the degree of iron falses, and the machine's ability to help you identify them. If you mean "seeing good stuff amongst iron," then I can't comment, but I certainly don't think I am tricked by MORE deep rusty iron than I was with my F-70 (though that was possibly due more to the "novice behind the wheel," as opposed to the machines themselves!)

Steve



Edited 1 time(s). Last edit at 05/20/2011 02:40AM by steveg.

When Sensitivity is increased........you are allowing the detector to amplify the most minute' of signals......including the noise. Some of the detectors available on the open market ALSO boost the volume of the audio report....on those minute' signals......which can REALLY give the illusion that Xmit power is increased.

NASA-Tom -- as I understand it, that's what the gain function does on the Minelab FBS machines. So are we saying that there is a level where a signal is weak enough that it is "ignored" by the machine, and this "ignore" level is set by sensitivity; then, if a weak signal falls above the "ignore" level, the gain function, when set "high," will amplify that weak signal's "audio report?"

Also -- still confused about how that "multiple frequency" thing fits in to all of this...

Steve

Half-truth. With a moderate Sens setting...........yes............a weak signal is ignored; hence, no audio report. Now..... the other half. IF the signal strength is 'just' above the minimum base-level req'd to audibly report..........this does not necessarily mean that it will be 'extra amplified'. What dictates this factor is....... if the detector is a 'modulated audio' platform..............or a 'amplified audio' platform. The 'modulated audio' platform will still allow this weak signal to audibly report as a low-volume/soft tone. Whereas a 'amplified audio' platform may take that weak signal.....and audibly boost it to a audio level of a shallow/loud target.

IRT multi-freq units; Iron is looked upon differently by each individual freq........some freq's of which are incongruent with other freq's; subsequently, confusing the unit.
Single-freq units are more of a 'yes' OR 'no' on a iron target. This is much less confusing for the operator and detector. A multi-freq unit.... can give a 'yes' AND 'no' ID response on iron targets.

Clear as mud?????

A little clearer than mud, so I thank you!

Gotcha on the "half-truth" part. I think my Fisher Gold Bug is a modulated audio platform; not sure on the Minelab; I think the gain allows you to adjust the "modulation" maybe? If gain is one, I think you get "highly-modulated" audio -- you hear quiet tones, louder tones, etc. When gain is maxed out at 10, I think all signals are amplified to sound the same -- shallow, or deep. So, is my Explorer some sort of "hybrid" in that you can adjust it, with the gain, from being sort of a "modulated audio" machine (gain setting of 1) all the way up to an "amplified audio" machine (gain setting of 10?)

As far as the "clear as mud" part -- would it be correct to say that in semi-auto sensitivity (which is known on the Explorers to be a more stable, better ID-ing way to run) that -- if the machine is hunting in iron, it "automatically" utilizes the "best" frequency, such that you get less "falsing" than you would by jacking up all three frequencies (which is what you do when you switch to manual sens.) In other words, forcing all three frequencies to a set level, which is what "manual" does, can result in a more confused, "falsy" machine, than if you hunt in semi-auto, where the machine can choose the "best" frequency when in iron (with the caveat that you may lose depth in semi-auto as a sacrifice for that more stable unit with better ID?)

Steve

Tom said it (almost), we may never know the whole truth about the matter.




I can (almost) positively say that ..... the 'Sensitivity' function of the Explorer/E-Trac still.......only adjusts the "Receive" sensitivity. I do not believe it alters (increases) 'transmit' power. This would be a 'more parts' and 'more expensive' function. I don't have blueprints of the Minelab(s)....... but can't imagine Transmit power being changed ... with the Sensitivity function.

Tom, Does the size of the send and receive coils (amount or volume of wire used), have something to do with; when increasing sens, it's designed to only boost the receive coil? Maybe power consumption?

I would not call the Minelab a 'hybrid'......IRT it giving you the ability to adjust the 'modulated' audio. The CZ-5, 6, 6a, 7, 7a, 7a Pro, 70, 20, 21, 3D is a 'modulated' audio system when Volume is '5' or below. When you increase the volume above '5'......the faint signals become loud.........including..........up to full volume audio.......when the volume control is max'ed out. And this is only one example. MANY other detectors incorporate this type of option.

And Steve.............you bring up a interesting caveat......IRT semi-auto function on Minelab. The detector will select (a very conservative) Sens setting................and...............when in heavy iron/nails.............the unit will select (conservatively) the best Freq(s) AND the best Sens........so as to allow to "maximum 'see' the iron" ability. This is NOT what you want................that being; a detector that is MOST resonant (tuned) to iron. You do NOT want a detector that is 'HOT' on iron. YET.............YET...............YET.............this is what the detector wants to do............and does provide one major attribute. When the detector selects the best/maximum settings to detect-and-see the iron............it will THEN "ID" the iron with higher accuracy. Not a bad trade-off. Catch 22!

Coils are an ENTIRE art-work unto themselves. ((( I do believe we need to put more 'intelligence' into coil design. ))) They do not have anything to do with 'volume'...................rather..................inductive coupling. Amount of 'windings'............size of 'windings' (coil size)............configuration of windings...............size/gauge of wire utilized....................winding capacitance......................inductance.....................shield-paint (and all of the variable properties that ensue IRT this shield-paint....how much, where, how deep, what type) ...........................coil wire length/inductance/capacitance/diameter/shielding/dielectric-rating/impedance............and a LOT more. Noteworthy of mention: the detector will have a 'Max-que' optimal performance setting that is most resonant to/for the coil. It is not a arbitrary point. And it will differ from one coil to another.

Engineering.

1. Knowing the 'known'.
2. Knowing there are 'unknowns'.
3. Knowing: You don't know...what you don't know.

You can not 'measure' the unknown. Therefore; you cannot 'engineer' .... or .... 're-engineer' the unknown. Sooooooo; How do you know what you are missing...................if you don't know it even exists.

Science.

Sooooooo; How do you know what you are missing...................if you don't know it even exists.

Intuition

I am a big believer in intuition by scientists/inventors................along with 'accidental' scientific discoveries.

NASA-Tom,

Thanks for the SUPER in-depth answer.

With respect to your discussion about semi-auto vs. manual...that's fascinating about how in semi-auto the detector ends up "making itself resonant to iron (bad), but with the POSITIVE attribute that it then IDs the iron better (possibly making the job of sorting the goodies from the iron in an iron trash-filled spot easier). Obviously, this raises the question of "OK, now how do I know which way and when, to run my machine?" Obviously, this is where experience comes in; my only question then would be -- does it make sense as a general approach, given my understanding of what you have explained, to utillize semi-auto sens. when in heavy iron trash (i.e. when you are getting a very unstable threshold, lots of sustained nulling) -- in that YES, that lower sensitivity setting is not the deepest, hottest setup, BUT you can't achieve max depth ANYWAY due to the iron. Meanwhile, when in cleaner ground, and you want to be able to hit max depth for deep targets, use high levels of manual sensitivity?

Thanks so much for this description/explanation. This helps me really understand the machine better, and what it's trying to do. This is why I LOVE this site!

Steve

Be careful. When the Minelab becomes more 'resonant' to iron.........giving the unit a better chance at accurate ID of the iron.........the unit is now no-longer 'resonant' for silver coins and/or high conductors.

Yes, manual Sens ...... and at higher levels.......is the ticket for clean/clear/sans-trash ground. This holds true for nearly all detectors.....regardless of brand.

NASA-Tom --

So, how do you "combat" that? Running manual sensitivity I guess would keep the "silver resonant" frequency's sensitivity high...but at the cost of more falsing; I guess the answer is, to simply "deal with" the falsing? Maybe run manual, but if you get a hit that you are not sure of -- maybe a false, maybe not -- that you want to decipher/interrogate, then switch over the semi-auto and re-scan the target (and see if the machine can better ID the target?)

Steve

You got it. Run semi-auto.............then run manual Sens.........over the same turf. There will be a learning-curve as to what/how-much manual Sens to run. All sites are different!

Thanks much. It does take awhile to master these Minelabs...

Steve

I FOUND THIS ON A ANOTHER SITE, BUT COULD NOT COPY AND PAST THE PICTURE.
BUT, YES, YOU WERE RIGHT TOM.
NO CHANGE IN THE TRANSMIT SIGNAL


I monitored the transmitted signal with my oscilloscope.
The signal is pictured below.
This signal did not change for any setting except when selecting NOISE CANCEL. NOISE CANCEL slightly offsets the transmitted/received signal frequency either manually via the menu or automatically by pushing the NOISE CANCEL button (which automatically selects the quietest frequency).
All other settings affect how the received signal is processed by the computer.

THE TRANSMITTED SIGNAL AMPLITUDE REMAINS CONSTANT.

Mark.....THANKS for taking the time to 'validate' .... utilizing a O-Scope!

Definitive answer -- perfect!

Thanks, markg.

Interesting that increasing sensitivity definitely seems to have a larger, direct effect on increasing "apparent" depth, much more than on my Fisher machines...

Steve

This is the most informative site on the web. Thanks to all the many experienced hunters and Tom for taking time out of their lives to explain and educate us all.
This site has greatly reduced my learning curve, but I'm not sure anyone can ever master any machine.